# CVE-2020-26265: Consensus flaw during block processing

> A consensus flaw in Geth causes a chain split, leading to denial of service by refusing the canonical chain; users must upgrade.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Dec 2020
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-xw37-57qp-9mm4, GO-2021-0105

## What is CVE-2020-26265?

CVE-2020-26265 is a medium-severity vulnerability in go-ethereum, published on 11 Dec 2020. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Go Ethereum, or "Geth", is the official Golang implementation of the Ethereum protocol. In Geth from version 1.9.4 and before version 1.9.20 a consensus-vulnerability could cause a chain split, where vulnerable versions refuse to accept the canonical chain. The fix was included in the Paragade release version 1.9.20. No individual workaround patches have been made -- all users are recommended to upgrade to a newer version.

Weakness: CWE-682 (Incorrect Calculation)

## Which versions are affected by CVE-2020-26265?

3 open source packages ship an affected version, including github.com/ethereum/go-ethereum. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/ethereum/go-ethereum` | Go | From 1.9.4 | 1.9.20 |
| `github.com/ethereum/go-ethereum` | Go | From 1.9.4 | 1.9.20 |
| `github.com/ethereum/go-ethereum` | Go | From 1.9.4 | 1.9.20 |

Products: Ethereum Go Ethereum.

## How do I fix CVE-2020-26265?

Upgrade github.com/ethereum/go-ethereum to 1.9.20 or later.

## Is CVE-2020-26265 being exploited?

There is no known exploitation of CVE-2020-26265 in the wild and no public exploit code.

## Other vulnerabilities in go-ethereum

- [CVE-2026-26314](https://insights.sbomify.com/CVE-2026-26314/): Go Ethereum affected by DoS via malicious p2p message (high 8.7)
- [CVE-2023-42319](https://insights.sbomify.com/CVE-2023-42319/): go-ethereum vulnerable to denial of service via crafted GraphQL query (high 7.5)
- [CVE-2023-40591](https://insights.sbomify.com/CVE-2023-40591/): Denial of service via malicious p2p message in go-ethereum (high 7.5)
- [CVE-2021-42219](https://insights.sbomify.com/CVE-2021-42219/): Denial of service in go-ethereum (high 7.5)
- [CVE-2022-23327](https://insights.sbomify.com/CVE-2022-23327/): Denial of Service in Go-Ethereum (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-26265 and fix it if it is affected.

What it is: CVE-2020-26265 is a medium-severity vulnerability in go-ethereum, published on 11 Dec 2020. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2020-26265 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/ethereum/go-ethereum (Go): affected from 1.9.4; fixed in 1.9.20
- github.com/ethereum/go-ethereum (Go): affected from 1.9.4; fixed in 1.9.20
- github.com/ethereum/go-ethereum (Go): affected from 1.9.4; fixed in 1.9.20

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2020-26265/ (Markdown: https://insights.sbomify.com/CVE-2020-26265/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-26265
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-26265
- OSV: https://osv.dev/vulnerability/CVE-2020-26265

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-26265/
Summaries are generated and may contain mistakes; the official description above is the record.